Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.32	12.241%	$55.3573	$55.36	$55.35	$55.40
Purchase #2	$154.41	12.332%	$173.4518	$173.45	$173.45	$173.50
Purchase #3	$122.36	11.628%	$136.588	$136.59	$136.60	$136.60
Purchase #4	$167.49	10.318%	$184.7716	$184.77	$184.75	$184.80
Purchase #5	$178.27	3.228%	$184.0246	$184.02	$184.00	$184.00
Purchase #6	$112.56	10.504%	$124.3833	$124.38	$124.40	$124.40
Purchase #7	$49.50	11.729%	$55.3059	$55.31	$55.30	$55.30
7 purchase totals =	$833.91		$913.8825	$913.88	$913.85	$914.00